The histochemistry of the saccus vasculosus in red-bellied Piranha, Pygocentrus nattereri Kner, 1858

The presence of mucopolysaccharides, glycogen, protein, and lipid component in the cellular constituents of saccus vasculosus of Pygocentrus nattereri Kner, 1858 were demonstrated histochemically using light microscopy. The saccus vasculosus was richly vascularized and comprised of a number of loculi enclosed by blood sinusoids. The loculi contained predominant coronet cells and supporting cells. Plenty of secretory materials were observed in the lumen. Periodic acid Schiff's reaction in combination with Alcian blue for mucopolysaccharides was positive for the apical protuberances of coronet cells and secretory matters in the lumen. Significant amounts of glycogen and protein were localized in coronet cells and blood cells. The coronet cells along with luminar protrusion contained an appreciable amount of DNA and RNA. Lipid is notably detected through Sudan black reaction in globular protrusion of coronet cells. The silver reaction was employed to investigate the presence and distribution of neurons within the epithelial lining as well as other regions of the saccus vasculosus. These histochemical tests revealed that the saccus vasculosus served dually as both a secretory and sensory organ.